Studio Technologies 230 2008 - Manual (Page 37)

Model 230 User Guide Issue 7, October 2008
Studio Technologies, Inc. Page 37
Talkback-to-Intercom Sidetone
Adjustment
Associated with the talkback-to-intercom
functions are null/sidetone trim potentiom-
eters that are used to adjust the talkback
levels that are being returned to the inter-
com line receive audio sources. These
two trim pots are part of the analog hybrid
circuit that separates (“nulls”) talkback
audio from receive (“listen”) audio. If audio
from either or both of the intercom channels
is to be used as a headphone source, and
talkback to these intercom channels is also
desired, the sidetone trim pots may need to
be adjusted.
One trim pot is associated with the sidetone
level for each channel of the intercom in-
terface. Both are accessible on the bottom
of the Model 230’s enclosure, adjacent to
the trim pots associated with the line-level
inputs. Adjusting them is very simple, requir-
ing only a pair of ears and a screwdriver.
With the Model 230 configured as previously
described, activate one of the talkback-to-
intercom functions. Audio from the con-
nected microphone should be heard in the
configured headphone output channel(s).
Adjust the trim pot associated with the
active intercom channel so that the de-
sired sidetone level, relative to the intercom
receive level, is achieved. The adjustment
range is approximately 18 dB, with the
sidetone level increasing as the trim pot
is rotated in its clockwise direction. Now
change to the other intercom channel and
adjust its sidetone trim pot as desired.
Using the Model 230’s active sidetone
function, talkback audio will be routed to the
headphone outputs by means of dedicated
circuitry. If this is enabled be certain to place
the two intercom sidetone trim pots to their
fully counterclockwise positions. This will
minimize the increase in sidetone level
that will occur when both the active sid-
etone and talkback-to-intercom functions
are active. Additional details are provided
later in this user guide.
Technical Notes
Grounding and Shielding
As previously discussed in this user guide,
the pin 1 connections on the main and
line-level talkback outputs’ 3-pin male
XLR-type connectors are “floating,” i.e.,
not connected to anything within the
Model 230’s enclosure. Some audio ex-
perts might take offense to this, grousing
that this should have been left to the user
or installer to be connected or disconnect
as desired. However repeated field testing
found that floating pin 1 on these outputs
was the key to maintaining quiet audio.
From Fenway Park, to the Orange Bowl,
and then northwest to Husker Stadium,
lifting pin 1 did the trick.
A simple solution is available if an applica-
tion does require that a ground be avail-
able on the main and line-level talkback
outputs’ interconnecting cables. All Model
230 XLR-type connectors have a ground
connection that is made to the interfacing
connector’s metal “shell.” And most XLR-
type connectors have a pin or connection
point available to access its metal shell. By
connecting the cable shield to the mating
connector’s shell terminal, the common
connection typically found on audio inter-
connections is created.
IFB Channel Crosstalk
By the very nature of its design, a stan-
dard “wet” IFB circuit is prone to exhibit
cross-talk between its two audio channels.